Improvements in microelectronics have increased the demand for electrolytic cells that can be directly incorporated into electronic devices so as to produce a portable, finished package. As the improvements in microelectronics reduce the size of the electronic device, the space and weight allotted to a power supply within such device have likewise decreased. It is therefore important to maximize the power-per-unit space that a battery can provide, but at the same time, minimize weight and fully utilize the space allotted to a power supply within an electronic device. The use of flexible packaging to enclose an electrolytic battery or cell is one way to reduce the weight of a battery or cell, and such packaging lends itself to unusual shapes. Flexible packaging can still provide hermetic containment of a battery, and in addition, is lighter than traditional packaging, i.e., metal cans or molded plastic cases. Flexible packaging also conforms more easily to the shape of the battery structure.
The flexible packaging may be formed of a single layer of a polymer film or single layer of a metal foil, but is typically comprised of a multi-layer material having a polymer layer for toughness, a metal foil layer to form a hermetic barrier and a third layer of an adhesive or sealant material. This multi-layer material is dimensioned to be tightly wrapped, e.g., to be folded, around a battery or cell. Heat and pressure are typically applied to overlapping edges of the material to form a seal enclosing the cell or battery. Operations such as folding of the material and the tight wrapping necessary for efficient packaging of the battery or cell place considerable stress on the various layers forming the material. Such stresses may lead to cracks forming in the metal foil layer. Such cracks, in addition to "pinhole imperfections" that may exist in the foil, can destroy the hermeticity of the packaging and allow solvents to escape from the battery or water vapor and oxygen to penetrate into the battery. Increasing the thickness of the foil layer sufficiently to avoid hermeticity issues can require undesirable increases in weight, thickness, stiffness and cost.
The present invention overcomes these and other problems and provides a multi-layer, flexible material for forming a package for an electrochemical device such as an electrolytic battery or cell.